1. Field of the Invention
The present invention relates to an electrode assembly for a glass melting furnace. The furnace may be an upwardly open chamber formed of a refractory material for containment of glass to be melted. The electrode assembly has an elongated electrode body preferably of molybdenum to deliver electrical current to the glass in the furnace to heat the glass to a molten condition. The invention relates particularly to means for supporting the electrode and cooling the electrode.
2. Prior Art
U.S. Pat. No. 2,591,709 to Lubatti relates to a furnace for melting metal, wherein the metal is heated by an electrode suspended from an elongated hollow arm structure above the metal surface. The arm structure is connected to an electrical current source for supplying current to the electrode. Current radiates from the electrode through the metal in the furnace to heat and melt the metal.
The Lubatti patent relates to water-circulation means for cooling a current-carrying arm; water flows through a small diameter pipe extending within the arm. Water is discharged from the small diameter pipe into the end of the arm structure connected to the electrode, whereby the water then flows in a reverse direction through the annular space between the small diameter pipe and the inner surface of the arm structure which is hollow. The flowing water cools the hollow arm structure, thereby preventing overheating of the arm structure.
U.S. Pat. No. 4,965,812 to Sorg, et al. relates to a variation of the Lubatti apparatus applied to a glass melting furnace. Sorg, et al. describes apparatus wherein a current supply arm structure is a steel tube having a copper lining. The steel provides mechanical strength, and the copper lining provides the current conductivity.
A disadvantage of the Sorg, et al. apparatus is that the weight of the electrode is transmitted to the steel portion of the tube through the copper lining. There is danger that the copper will be distorted and adversely affect the current-carrying function and service life of the tube structure. Another disadvantage of the steel-copper composite tube is that the steel increases the overall electrical resistance of the tube so that less current is available to the electrode (unless the copper lining has a very large wall thickness).
A further disadvantage of the steel-copper composite tube is that the steel acts as a barrier to the escape of radiant heat from the outer surface of the copper lining so that relatively large coolant flow is required to maintain the copper lining at a satisfactory temperature range with minimal temperature variation in the copper). A related disadvantage is that copper has a significantly higher coefficient of thermal expansion than steel, so that there can be produced thermally-induced stresses in the composite tube, with potentially shortened tube service life. Relatively high cost of the composite tube is a further disadvantage.